function s =subim(f,m,n,rx,cy)
%SUBIM Extracts a subimage, s, from a given image, f.
% The subimage is of size m-by-n, and the coordinates
% of its top, left corner are (rx, cy).

s = zeros(m,n);
rowhigh = rx+m-1;
colhigh = cy+n-1;
xcount = 0;
for r = rx:rowhigh
    xcount = xcount+1;
    ycount = 0;
    for c = cy:colhigh
        ycount = ycount + 1;
        s(xcount, ycount) = f(r, c)
    end
end
